This relay automatically senses the condition of the towing vehicles alternator and diverts some of the current charging it’s battery to the caravan’s battery or fridge as well. This happens automatically when sensors trigger a split charge relay at a set voltage. This does not require a separate lead from the ignition switch as the switch in the relay is automatic.

It is important to use cables with sufficient stranding to prevent voltage drop as this can stop the relay from functioning. Cable that has a minimum stranding of 35/0.3 (2.5 sq mm) should be suitable for the 12v feed from the battery to the relay. Cable with a minimum stranding of 16/0.2 (0.5 sq mm) should be enough for the earth.

Comment Pages

I had a 25amp relay @ £10, which I fitted 3 years ago. It finally blew out, first noticed when it refused to operate the fridge. I also had 2 spare batterries (72amp + 75amp = 147amp) which I have been using for a rare jump start, on the same split charger. My trailer batterry is a 110amp. A battery salesman told me that I am simply asking to much, and advised a 30amp split charger.